Much of the joint damage in RA is caused by the synovium-the lining of the joint. In RA, the synovium increases in size and destroys bone and cartilage. The synovium maintains its growth by forming many new small blood vessels to nourish it. New drug treatments are being developed to stop the growth of these new blood vessels. The effect of these treatments on the synovium is usually measured by performing a biopsy-removing a small piece of synovium for examination under a microscope. The biopsy requires inserting a needle into the joint to withdraw the synovial tissue. This study will see if changes in blood flow can be assessed accurately using noninvasive imaging procedures, such as PET scanning, instead of a biopsy.